Field of the Invention
Embodiments of the present invention relate generally to a multi charged particle beam writing method and a multi charged particle beam writing apparatus, and more specifically, for example, relate to a method for reducing the writing time of multi-beam writing by tracking deflection.
Description of Related Art
In recent years, with high integration of LSI, the line width (critical dimension) required for circuits of semiconductor devices is becoming progressively narrower. As a method for forming an exposure mask (also called a reticle) used to form circuit patterns on these semiconductor devices, the electron beam (EB) writing technique having excellent resolution is employed.
As an example employing the electron beam writing technique, a writing apparatus using multiple beams (multi-beams) can be cited. Compared with the case of writing a pattern by using a single electron beam, since it is possible to emit multiple beams at a time (one shot) in multi-beam writing, the throughput can be greatly increased. For example, in a writing apparatus employing a multi-beam system, multiple beams are formed by letting portions of an electron beam emitted from an electron gun assembly pass through a corresponding hole of a plurality of holes formed in the mask, blanking control is performed for each beam, and each unblocked beam is reduced by an optical system and deflected by a deflector so as to irradiate a desired position on a target object or “sample”.
In multi beam writing, a high-speed throughput can be realized as described above. The shorter the one shot cycle of multi-beams is, the higher the throughput becomes. Conventionally, pixels are defined by dividing a writing region in the surface of the target object into a plurality of mesh regions by the beam size. Then, during irradiation of multiple beams of each shot to the target object placed on the stage moving at a fixed speed, each beam irradiation is executed while each beam performs a tracking operation following the stage movement so that a pixel to be irradiated by each beam may not be displaced by the stage movement. After one shot, the tracking operation is reset to swing back each beam, and the deflection position is shifted to a next pixel to be irradiated. Then, in the same way as described above, each beam irradiation is performed while executing the tracking operation. Thus, a pattern is written by performing necessary beam irradiation for each of the entire pixels.
In order to avoid a glitch generated in amplifiers for deflectors used for performing a tracking operation, a low pass filter (LPF) is built in each amplifier. For performing a highly accurate tracking operation, it is necessary to use an output signal having passed through the LPF in the tracking operation. In that case, a long stabilization period (settling time) is needed for the amplifier for tracking, in order to reset the tracking operation and shift to a next tracking operation. As the settling time, for example, 10% or more of the maximum irradiation time (maximum exposure time) of each beam is needed. Therefore, there is a problem that the settling time for resetting the tracking operation degrades the writing speed and further, the throughput.
In connection with the multi-beam technique, there is disclosed a technique where a tracking operation in response to a stage movement is performed while multi beams are continuously scanned in one direction by the raster scan method (refer to, e.g., Japanese Published Unexamined Patent Application (JP-A) No. 05-166707).